Apparatus and method for controlling uplink transmission power in a multiple element carrier wave system

ABSTRACT

The present invention relates to an apparatus and method for controlling uplink transmission power in a multiple element carrier wave system. The method for controlling uplink transmission power by a terminal in a multiple element carrier wave system includes the steps of: generating an uplink signal to be transmitted in a first serving cell; receiving, from a base station, random access start information for commanding the start of a random access procedure for a second serving cell; calculating the estimated surplus power from first transmission power scheduled for an uplink signal transmission, and second transmission power scheduled for a transmission of a PRACH to which a random access preamble is mapped; and when the estimated surplus power is smaller than a threshold power, adjusting the first transmission power or the second transmission power on the basis of power allocation priority.

CROSS REFERENCE TO RELATED APPLICATIONS

This application continuation of U.S. patent application Ser. No.14/357,557 filed on May 9, 2014, which is the National Stage Entry ofInternational Application PCT/KR2012/009177, filed on Nov. 2, 2012 andclaims the priority from and the benefit of Korean Patent ApplicationNo. 10-2011-0119154, filed on Nov. 15, 2011, all of which areincorporated herein by reference for all purposes as if fully set forthherein.

BACKGROUND Field

The present invention related to wireless communication and moreparticularly, an apparatus and method for controlling uplinktransmission power in a multiple component carrier system.

Discussion of the Background

The 3^(rd) Generation Partnership Project (3GPP) Long Term Evolution(LTE) and IEEE (Institute of Electrical and Electronics Engineers)802.16m technology are under development as candidates for the nextgeneration wireless communication technology. The IEEE 802.16mspecification not only supports compatibility with legacy systems byrelying on a revision of the existing 802.16e specification but alsosecures continuity towards a future technology meant for the nextgeneration. IMT-Advanced system. Therefore, the 802.16m specificationsare required to meet advanced requirements for the IMT-Advanced systemwhile maintaining compatibility with Mobile WiMAX systems based on the802.16e specifications.

Most wireless communication systems make use of one frequency band fordata transmission. For example, the 2^(nd) wireless communication systemuses a frequency band in the range of 200 KHz to 125 MHz while the3^(rd) wireless communication system uses a frequency band ranging from5 MHz to 10 MHz. To support ever-increasing transmission throughput, thelatest 3GPP LTE or 802.16m is increasing frequency bandwidth up to 20MHz or more. Increasing bandwidth is essential to deal with hightransmission throughput, but large power consumption is caused tosupport large bandwidth even when required communication service qualityis low.

In this regard, a multiple component carrier system is emerging, whichdefines a carrier having one frequency band and a center frequency andenables broadband transmission and/or reception of data through multiplecarriers. In other words, by using one or more carriers, narrow andbroad band are supported at the same time. For example, if a carrieruses a bandwidth of 5 MHz, a maximum of 20 MHz can be supported byutilizing four carriers of the is same kind.

One way for a base station to utilize the resources of a user equipmentin an efficient manner is to utilize information about power of the userequipment. Power control technology is essential to minimize inferencefactors for efficient distribution of resources in wirelesscommunication and to reduce battery consumption of a user equipment. Auser equipment can determine uplink transmission power according toscheduling information such as Transmit Power Control (TPC) allocated bya base station, Modulation and Coding Scheme (MCS), and frequencybandwidth.

Since uplink transmission power of a component carrier has to be takeninto account in a comprehensive manner as a multiple component carriersystem is introduced, power control of a user equipment becomes morecomplicated. This complexity can bring about a problem in view ofmaximum transmission power of the user equipment. In most cases, theuser equipment should operate based on the power lower than maximumtransmission power within an allowable range. If a base station performsscheduling requiring transmission power more than the maximumtransmission power, actual uplink transmission power may exceed themaximum transmission power, leading to a problematic situation. This isso because power control of multiple component carriers is notexplicitly defined or information about uplink transmission power is notfully shared between the user equipment and the base station.

SUMMARY

An object of the present invention is to provide an apparatus and amethod for controlling uplink transmission power in a multiple componentcarrier system.

Another object of the present invention is to provide an apparatus and amethod for allocating transmission power to a physical uplink channel ina plurality of service cells.

A yet another object of the present invention is to provide an apparatusand a method for determining a priority of allocating transmission powerin a physical uplink channel in a plurality of serving cells.

Solution to the Problem

According to one aspect of the present invention, a method forcontrolling uplink transmission power by a user equipment in a multiplecomponent carrier system is provided. The method for controlling uplinktransmission power comprises generating an uplink signal to betransmitted on a first serving cell, receiving from a base stationrandom access start information commanding start of a random accessprocedure for a second serving cell; calculating estimated powerheadroom from second transmission power scheduled for transmission of aPhysical Random Access Channel (PRACH) to which a random access preambleis mapped; and in case the estimated power headroom is smaller than athreshold, adjusting the first transmission power or the secondtransmission power based on a power allocation priority.

When an uplink signal is to be transmitted in a multiple componentcarrier system, uplink transmission power can be distributed in anefficient manner if the uplink signal is transmitted selectivelyaccording to a priority order of power allocation. Also, since power isdistributed according to a simple but clear rule, system performance canbe improved while reducing system complexity at the same time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one example of a wireless communication system towhich the present invention is applied;

FIG. 2 illustrates intra-band contiguous carrier aggregation while FIG.3 illustrates intra-band non-contiguous carrier aggregation and FIG. 4illustrates inter-band carrier aggregation;

FIG. 5 illustrates linkage between a downlink component carrier and auplink component carrier in a multiple component carrier system;

FIG. 6 illustrates one example of a graph showing power headroom of thepresent invention along time-frequency axis;

FIG. 7 is a flow diagram illustrating a method for controlling uplinktransmission power by a user equipment according to one example of thepresent invention;

FIG. 8 is a flow diagram illustrating a method for controlling uplinktransmission power by a user equipment according to another example ofthe present invention;

FIG. 9 is a flow diagram illustrating a method for controlling uplinktransmission power according to one example of the present invention;and

FIG. 10 is a block diagram illustrating a user equipment and a basestation controlling uplink transmission power according to one exampleof the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

In what follows, a few embodiments according to the present inventionwill be described in detail with reference to accompanying drawings. Itshould be noted that in assigning reference symbols to the respectiveconstituting elements, the same symbols are used for the sameconstituting elements as possibly as can be throughout the documentthough they may be found in different drawings. Also, for the sake ofdescribing embodiments of the present invention, if it is determinedthat specific descriptions about a structure or a function known to thecorresponding technical field unnecessarily obscures the technicalprinciples of the present invention, the corresponding descriptions willbe omitted.

This document is related to a wireless communication network. It isassumed that tasks of a wireless communication network can be carriedout by a system supervising corresponding wireless communication network(for example, a base station) while controlling the network andtransmitting data, or the tasks can be carried out by a user equipmentconnected to the corresponding wireless communication network.

FIG. 1 illustrates one example of a wireless communication system towhich the present invention is applied.

With reference to FIG. 1, the wireless communication system 10 isdeployed in wide areas to provide various kinds of communicationservices such as a voice and packet data service.

The wireless communication system 10 comprises at least one Base Station(BS) 11. Each BS 11 provides communication services intended for aparticular geographic region (which is usually called a cell) 15 a, 15b, 15 c. A cell can be divided into a plurality of sub-regions (whichare called sectors).

A User Equipment (LE) 12 may be stationary or mobile and can be referredto by different terms such as a Mobile Terminal (MT), User Terminal(UT), Subscriber Station (SS), wireless device, Personal DigitalAssistant (PDA), wireless modem, handheld device, and the like.

The BS 11 usually refers to a station communicating with the UE 12 andcan be referred to by different terms such as an evolved-NodeB (eNB),Base Transceiver System (BTS), access point, and the like, it should benoted that a cell is a generic term indicating a local area covered bythe BS 11 and represents various types of cells, including a megacell,macrocell, macrocell, picocell, femtocell, and the like.

In what follows, downlink transmission denotes communication from the BS11 to the UE 12, and uplink transmission denotes communication from theUE 12 to the BS 12. In the downlink transmission, a transmitter can be apart of the BS 11 while a receiver can be a part of the UE 12.

In the uplink transmission, a transmitter can be a part of the UE 12while a receiver can be a part of the base station 11.

There is no limitation on the multiple access techniques used for awireless communication system. Various multiple access techniques suchas Code Division Multiple Access (CDMA), Time Division Multiple Access(TDMA), Frequency Division Multiple Access (FDMA), Orthogonal FrequencyDivision Multiple Access (OFDMA), Single Carrier-FDMA (SC-FDMA),OFDM-FDMA, OFDM-TDMA, and OFDM-CDMA can be used. For uplink and downlinktransmission, a Time Division Duplex (TDD) technique can be used, whichcarries out data transmission by using different time slots or aFrequency Division Duplex (FDD) technique can be used, which carries outdata transmission by using different frequency bands.

Layers of a radio interface protocol between a UE and a network can beclassified into L1 (first layer), L2 (second layer), and L3 (thirdlayer) based on the lower three layers of the to Open SystemInterconnection (OSI) model widely accepted by communication systems.

The physical layer, which is the first layer, is connected to a MediaAccess Control (MAC) layer, located above the physical layer, through atransport channel. Data is transferred between the MAC layer and thephysical layer through the transport channel. Data transfer betweendifferent physical layers, namely between the respective physical layersof transmitting and receiving sides, is performed through the physicalchannel. A few physical control channels are available for data transferbetween physical layers.

A Physical Downlink Control Channel (PDCCH), which performs transfer ofphysical control information, informs the UE about resource allocationof a Paging Channel (PCH) and Downlink Shard Channel (DL-SCH) and HybridAutomatic Repeat Request (HARQ) information related to the DL-SCH. ThePDCCH transports a uplink grant which informs the UE about resourceallocation of uplink transmission. A Physical Control Format IndicatorChannel (PCFICH) informs the UE about the number of OFDM symbols usedfor PDCCHs and is transmitted for each subframe. A Physical Hybrid ARQIndicator Channel (PHICH) transports a HARQ ACK/NACK signal in responseto uplink transmission.

A Physical Uplink Control Channel (PUCCH) transports the HARQ ACK/NACKsignal about downlink transmission, a scheduling request, and uplinkcontrol information such as Channel Quality Information (CQI). APhysical Uplink Shared Channel (PUSCH) transports a Uplink Shared.Channel (UL-SCH).

The UE transmits a PUCCH or a PUSCH as follows.

The UE forms a PUCCH with respect to at least one of the informationabout Precoding Matrix Index (PMI) or Rank Indicator (RI) selected basedon CQI or measured spatial channel information and transmit the PUCCHperiodically to the BS. Also, the UE, after receiving downlink data,transmits Acknowledgement/Non-Acknowledgement (ACK/NACK) informationabout the received downlink data to the BS after a predetermined numberof subframes. As one example, in case the UE receives downlink data atthe n-th subframe, the UE transmits a PUCCH, which includes ACK/NACKinformation about the downlink data, at the (n+4)-th subframe. If the UEis incapable of transmitting all of the ACK/NACK information on thePUCCH allocated by the BS or the BS does not allocate the PUCCH throughwhich the ACK/NACK information can be transmitted, the UE can transmitthe ACK/NACK information through the PUSCH.

The radio datalink layer, which is the second layer, consists of an MAClayer, an RLC layer, and a PDCP layer. The MAC layer is responsible formapping between a logical channel and a transport channel, selects anappropriate transport channel to transmit data transferred from the RLClayer, and adds necessary control information to the header of the MACProtocol Data Unit (PDU). The RLC layer, located above the MAC layer,supports reliable transmission of data. Further, the RLC layer segmentsand concatenates RLC Service Data Units (SDUs) transferred from an upperlayer so that data can be configured to have a size suitable for awireless section. The RLC layer at a receiver supports a data reassemblyfunction to restore the original RLC SDU from the received RLC PDUs. ThePDCP layer is used only in a packet exchange region. To increasetransmission efficiency of packet data in a radio channel, the PDCPlayer transmit data by compressing a header of an IP packet.

The Radio Resource Control (RRC) layer, the third layer, exchanges radioresource control information between the UE and the network along with afunction of controlling a lower layer. Depending on a communicationcondition, the RRC state can be defined in various ways, such as an idlemode and RRC connected mode. In the RRC layer, various proceduresrelated to radio resource management are defined, including a systeminformation broadcasting procedure, RRC connection management procedure,multiple component carrier configuration procedure, radio bearer controlprocedure, security procedure, measurement procedure, and mobilitymanagement procedure (handover).

Carrier aggregation (CA) supports a plurality of component carriers andis is alternatively called spectrum aggregation or bandwidthaggregation. An individual carrier wave grouped together by carrieraggregation is called a component carrier (in what follows, it is calledCC). Each CC is defined by its bandwidth and center frequency. Carrieraggregation is employed to support growing throughput, prevent increaseof costs due to broadband RF (Radio Frequency) devices, and ensurecompatibility with the existing systems. For example, if five CCs areallocated with granularity of 5 MHz bandwidth for each carrier, amaximum of 25 MHz bandwidth can be supported.

Carrier aggregation can be classified into intra-band contiguous carrieraggregation of FIG. 2, intra-band non-contiguous carrier aggregation ofFIG. 3, and inter-band carrier aggregation of FIG. 4.

First of all, with reference to FIG. 2, intra-band contiguous carrieraggregation is carried out among contiguous CCs in the same band. Forexample, CC#1, CC#2, CC#3, . . . , CC#N, which are component carriers tobe aggregated, are all contiguous to each other.

With reference to FIG. 3, intra-band non-contiguous carrier aggregationis performed for non-contiguous CCs. For example, CC#1 and CC#2, whichare component carriers to be aggregated, are placed away from each otherby a predetermined frequency.

With reference to FIG. 4, inter-band carrier aggregation refers to thesituation where multiple component carriers exist and one or morecomponent carriers are aggregated in a different frequency band. Forexample, among component carriers to be aggregated, CC#1 belongs to aband#1 while CC#2 belongs to a band#2,

The number of CCs aggregated can be set differently for downlink anduplink transmission. Symmetric aggregation refers to the case where thenumber of downlink CCs is the same as the number of uplink CCs, whileasymmetric aggregation refers to the case whether the number of CCs fordownlink transmission is different from that for uplink transmission.

Also, the size of CCs (namely, bandwidth) can be different from eachother. For example, suppose five CCs are used to construct a frequencyband of 70 MHz. Then, the frequency band of 70 MHz can be configured byusing 5 MHz CC (carrier #0), 20 MHz CC (carrier #1), 20 MHz CC (carrier#2), 20 MHz CC (carrier #3), and 5 MHz CC (carrier #4).

A multiple component carrier system refers to a system supportingcarrier aggregation. The multiple component carrier system can employcontiguous carrier aggregation or non-contiguous carrier aggregation.Also, either of symmetric and asymmetric aggregation can be used for themultiple component carrier system.

FIG. 5 illustrates linkage between a downlink component carrier and auplink component carrier in a multiple component carrier system.

With reference to FIG. 5, as one example, a downlink component carrier(hereinafter, DL CC) D1, D2, and D3 are aggregated; and uplink componentcarrier (hereinafter, UL CC) U1, U2, and U3 are aggregated. At thistime, Di is an index of DL CC while Ui is an index of UL CC (i=1, 2, 3).At least one DL CC is PCC and the others are SCC. It should be notedthat the index does not necessarily correspond to an order of acomponent carrier or position of frequency band of the correspondingcomponent carrier.

Meanwhile, at least one UL CC is PCC and the others are SCC. Forexample, D1 and U1 are PCC while D2, U2, and U3 are SCC.

At this time, the index of a primary component carrier can be set to 0,and one of the natural numbers can be an index of a secondary componentcarrier. Also, the index of the downlink or uplink component carrier canbe set to the same index of a component carrier (or a serving cell)including the corresponding downlink or uplink component carrier. Asanother example, only the component carrier index or secondary componentcarrier index is defined, but an index for the downlink or uplinkcomponent carrier included in the corresponding component carrier maynot be defined at all.

In an FDD system, one-to-one linkage can be established between the DLCC and UL CC. For example, D1 is one-to-one liked to U1 while D2 to U2;and D3 to U3. Through the system information transmitted by a logicalchannel BCCH or a UE-specific RRC message transmitted by a DCCH, the UEestablishes linkage among the DL CCs and the UL CCs. Such linkage iscalled System Information Block (SIB) 1 linkage or SIB2 linkage. The UEcan establish linkage in a cell-specific manner or UE-specific manner.As one example, the primary component carrier is configured in acell-specific manner while the secondary component carrier is configuredin a UE-specific manner. At this time, one-to-one, one-to-n, or n-to-onelinkage can be established between the downlink component carrier andthe uplink component carrier.

A downlink component carrier corresponding to a Primary Serving Cell(PSC) is called a Downlink Primary Component Carrier (DL PCC) while auplink component carrier corresponding to the PSC is called a UplinkPrimary Component Carrier (UL PCC), Similarly, in the case of downlinktransmission, a component carrier corresponding to a Secondary ServingCell (SSC) is called a Downlink Secondary Component Carrier (DL SCC)while, in the case of uplink transmission, a component carriercorresponding to the secondary serving cell is called a Uplink SecondaryComponent Carrier (UL SCC) One serving cell may include only the DL CCsor both of DL CCs and UL CCs.

The primary serving cell and the secondary serving cell arecharacterized as follows.

First, the primary serving cell is used for transmission of the PUCCH.

Second, the primary serving cell is always activated whereas thesecondary serving cell is a carrier activated or deactivated dependingon a particular condition.

Third, when the primary serving cell experiences a Radio Link Failure(RLF), RRC re-connection is triggered, but when the secondary servingcell experiences the RLF, RRC re-connection is not triggered.

Fourth, the primary serving cell can be changed when a security key ischanged or by a handover procedure which accompanies a Random AccessChannel (RACH) procedure. It should be noted that in the case of MSG4(contention resolution), only the PDCCH which commands the MSG4 has tobe transmitted through the primary serving cell and MSG4 information canbe transmitted through the primary serving cell or the secondary servingcell.

Fifth, Non-Access Stratum (NAS) information is received through theprimary serving cell.

Sixth, in the primary serving cell, the DL PCC and the UL PCC alwaysform a pair.

Seventh, each UE can set a different component carrier as the primaryserving cell.

Eighth, the RRC layer can carry out a procedure such as reconfiguration,adding, and removal of the secondary serving cell. In adding a newsecondary serving cell, RRC signaling can be used to transmit systeminformation of a dedicated secondary serving cell.

The technical principles of the present invention related to thecharacteristics of the primary and the secondary serving cell are notnecessarily limited to those described above, but the descriptions aboveare only an example and further examples can be included within thetechnical principles of the present invention.

A plurality of serving cells can be configured for a single UE. Forexample, the UE can be configured for the primary serving cell and onesecondary serving cell, or for the primary serving cell and a pluralityof secondary serving cells. And a plurality of serving cells configuredfor the UE can transmit a uplink channel simultaneously or in parallelfashion. At this time, the uplink channel comprises a PUCCH, PUSCH, andPRACH. A RACH is mapped to the PRACH. The following illustrates anexample where a plurality of uplink channels is transmitted in parallelon a plurality of serving cells. As one example, the PUCCH and the PRACHcan be transmitted in parallel to the primary and the secondary servingcell, respectively. As another example, the PUSCH and the PRACH can betransmitted in parallel to the primary and the secondary serving cell,respectively.

To transmit a plurality of uplink channels on a plurality of servingcells, the UE requires power enough to transmit the plurality of uplinkchannels. However, it is often the case that maximum transmission powerallocated to the TIE is limited and is not enough to transmit all theuplink channels. For example, suppose the maximum transmission powerallocated to the UE is 10 W and 7 W and 5 W are needed to transmit thePUSCH and the PRACH respectively to the primary serving cell and thesecondary serving cell. Since transmission power of the PUSCH and thePRACH amounts to 12 W in total, 2 W is still needed to get the maximumtransmission power. Therefore, less power than required is allocated toeither of the PUSCH and the PRACH. To solve the problem above, the UEcan allocate given uplink transmission power to each channel based on apriority order, which is called a power allocation priority.

As one example, the UE allocates power of 10 W to either of the PUSCHand the PRACH and allocates the remaining power for transmission ofother channel. For example, in case the PUSCH has a high priority, theUE first allocates 7 W to the PUSCH and allocates the remaining 3 W tothe transmission of the PRACH. In this case, the power required fortransmission of the PUSCH is all allocated, but the power less than therequired for transmission of the PRACH by 2 W is allocated. On the otherhand, in case the PRACH has a high priority, the UE first allocates 5 Wto the PRACH and allocates the remaining 5 W to transmission of thePUSCH. In this case, the power less than the required for transmissionof the PUSCH by 2 W, but all of the power required for transmission ofthe PRACH is allocated.

The power allocation priority has been described with an example ofusing only the PUSCH and the PRACH, the power allocation priority can beassigned to all of physical uplink channels such as the PUCCH, PUSCH,PRACH, and SRS.

One factor which determines the power allocation priority is channelreliability. A higher power allocation priority is assigned to thechannel for which higher reliability needs to be secured. With morepower a signal is transmitted, with more reliability the signal can bereceived.

First, regarding reliability between the PUSCH and the PRACH, since theBS is capable of detecting Discontinuous Transmission (DTX) with respectto the PUSCH, system performance does not change much even if thereliability of the PUSCH is low. On the other hand, if the BS fails todetect the PRACH, system performance can be degraded as the BS is thenunable to respond promptly to the UE's request for uplink transmissionresources. In other words, the PRACH requires higher reliability thanthe PUSCH, and a higher power allocation priority can be assigned to thePRACH. However, in case at least one of ACK/NACK signal, Channel QualityInformation (CQI), and a rank indicator is transmitted through thePUSCH, the PUSCH can have an exceptionally higher power allocationpriority than the PRACH.

Second, regarding reliability between the PUCCH and the PRACH, since thePUCCH carries primary control information such as the ACK/NACK signal,channel state information, and rank indicator, the PUCCH has a higherreliability than the PRACH. This is so because if the BS fails toreceive the ACK/NACK signal with respect to downlink data, downlinktransmission or re-transmission is delayed successively, thereby causingsystem performance degradation. Therefore, of the PUCCH and the PRACH,the PUCCH has a higher power allocation priority.

Third, a Sounding Reference Signal (SRS) has the lowest power allocationpriority when compared with a physical uplink channel. The SRS is areference signal used for uplink scheduling. The UE sends the SRS to auplink channel, and the BS performs scheduling for uplink transmissionafter checking the uplink channel state from the SRS.

In what follows, Power Headroom (PH) is described in detail. PH denotespower left for the UE to use in addition to the power used for currentuplink transmission. For example, suppose the maximum transmission powerfor the UE is 10 W and the LIE is currently using 9 W of power in thefrequency band of 10 MHz. Since the UE can use additional power of 1 W,the power headroom becomes 1 W.

At this time, if the BS allocates a frequency band of 20 MHz to the UE,power of 18 W (=9 W×2) is required. Since the maximum transmission powerof the LYE is 10 W, however, either the UE cannot utilize the wholefrequency band of 20 MHz or the BS cannot receive the UE's signalreliably because of lack of power of the UE. To solve this problem, ifthe UE report to the BS that the PH is 1 W, the BS can performadditional scheduling in the range of the PH. The report is called PowerHeadroom Report (PHR).

PH is defined as a difference between the maximum transmission powerP_(cmax) configured for the UE and estimated power P_(estimated) withrespect to uplink transmission as shown in Eq. 1 and is expressed inunits of dB.

P _(PH) =P _(cmax) −P _(estimated) [dB]  [Equation 1]

In other words, power headroom P_(PH) is obtained as the power left fromthe maximum transmission power of the UE allocated by the BS byexcluding the P_(estimated) which is a sum of transmission power used byindividual serving cells. Meanwhile, the maximum transmission power canbe defined for each of the serving cells; for example, the maximumtransmission power of a serving cell c is represented by P_(cmax,c).

As one example, P_(estimated), equals the power P_(PUSCH,c) estimatedwith respect to transmission of the PUSCH in the serving cell c.Therefore, in this case, the PH can be obtained by using Eq. 2. Equation2 is related to the case where only the PUSCH is transmitted throughuplink transmission of the serving cell c, which is denoted as a type 1.The according to the type 1 is denoted by type 1 PH P_(PH,c-type1).

P _(PH,c-type1) =P _(cmax,c) −P _(PUSCH,c) [dB]  [Equation 2]

As another example, P_(estimated,c) equals a sum of the powerP_(PUSCH,c) estimated with respect to transmission of the PUSCH in theserving cell c and the power P_(PUCCH,c) estimated with respect totransmission of the PUCCH. Therefore, in this case, the PH can beobtained by using Eq. 3. Equation 3 is related to the case where thePUSCH and the PUCCH are transmitted through uplink transmission of theserving cell c at the same time, which is denoted as type 2. The PHaccording to the type 2 is denoted by type 2 PH P_(PH,c-type2). At thistime, the serving cell c includes the primary serving cell.

P _(PH,c-type2) =P _(cmax,c) −P _(PUCCH,c) −P _(PUSCH,c) [dB]  [Equation3]

FIG. 6 illustrates a graph showing PH according to Eq. 3 alongtime-frequency axis. FIG. 6 shows the PH with respect to one servingcell c.

With reference to FIG. 6, the maximum transmission power P_(cmax)configured for the UE consists of P_(PH) 605, P_(PUSCH) 610, andP_(PUCCH) 615. In other words, the remaining power from P_(cmax) byexcluding the P_(PUSCH) 610 and the P_(PUCCH) 615 is defined as P_(PH)605. Each of the power values is calculated in units of TransmissionTime Interval (TTI).

The primary serving cell is the only serving cell holding a UL PCCcapable of transmitting the PUCCH.

Since the secondary serving cell is incapable of transmitting the PUCCH,the PH is determined according to Eq. 2, but parameters and operationsof a method for reporting power headroom determined by Eq. 3 are notdefined. On the other hand, the operation and the parameters of a methodfor reporting power headroom determined by Eq. 3 can be defined in theprimary serving cell. In case the UE has to transmit the PUSCH in theprimary serving cell by receiving a uplink grant from the BS and thePUCCH is transmitted simultaneously to the same subframe according to apredetermined rule, the UE calculates the PH values according to Eqs. 2and 3 at the time the PHR is triggered and transmits the calculated PHvalues to the BS.

If the maximum transmission power is sufficiently large and the powerheadroom according to Eq. 2 or 3 is larger than 0 dB, it causes noproblem to transmit a plurality of physical uplink channels or SRS atthe same time to a plurality of serving cells. In this case, there is noneed to apply the power allocation priority.

The power allocation priority becomes important when the power headroomgets smaller than 0 dB as the UE transmits the PRACH in parallel on asecond serving cell at the time of transmitting the PUCCH, PUSCH, SRS,or PUCCH and PUSCH on a first serving cell. For example, in case the UEtransmits the PUSCH to the first serving cell, the power headroom iscalculated according to Eq. 2. In case the UE also has to transmit thePRACH to the second serving cell, however, the maximum transmissionpower P_(cmax) is decreased as much as the transmission power of thePRACH. This is so because the power coordination value, which is aparameter to reduce the size of the maximum transmission power P_(cmax),becomes large due to the PRACH. If P_(cmax) is reduced in Eq. 2, themagnitude of the power headroom gets smaller than 0 dB.

At this time, according to the power allocation priority, the UE has toselectively transmit either of the PUSCH and the PRACH or transmit bothof the PUSCH and the PRACH, but has to reduce transmission power ofeither of the two channels.

FIG. 7 is a flow diagram illustrating a method for controlling uplinktransmission power by a user equipment according to one example of thepresent invention.

With reference to FIG. 7, the UE generates an uplink signal scheduled tobe transmitted on a first serving cell of a first subframe S700. Theuplink signal includes, for example, a physical uplink channel or SRS.The physical uplink channel includes at least one of the PUSCCH and thePUSCH. Two or more serving cells are assigned to the UE, and the firstserving cell includes the primary serving cell.

The UE receives from the BS random access initiate information whichcommands initiation of a random access procedure on a second servingcell of the first subframe S705. The random access initiate informationis related to a second serving cell. The random access initiateinformation is defined in a form similar to Downlink Control Information(DCI). The DCI is mapped to the PDCCH and transmitted from the BS to theUE, which can be called a PDCCH order. The DCI can be a DCI format 1A,which is defined as shown in the following table.

TABLE 1 Carrier Indicator Field (CIF) - 0 or 3 bits. Flag foridentifying format 0/1A - 1 bit (format 0 in the case of 0 and format 1Ain the case of 1) In case format 1A CRC is scrambled with C-RNTI and theremaining fields are configured as described below, the format 1A isused for the random access procedure initiated by the PDCCH order. - Thefollowing - Localized/Distributed VRB allocation flag - 1 bit. The flagis set to 0. Resource block allocation ┌ log₂(N_(RB) ^(DL)(N_(RB)^(DL) + 1)/2 ┐ bits. All of the bits are set to 1. Preamble Index - 6bits PRACH mask index - 4 bits All of the remaining bits of the format1A intended to allocate a simplified schedule of one PDSCH codeword areset to 0.

With reference to Tale 1, depending on a value of the preamble index,the random access procedure initiated by an order of the BS can becarried out in a contention based manner or in a non-contention basedmanner. As one example, if six bits of the preamble index informationare all set to “0”, a contention-based random access procedure iscarried out. For example, if the preamble index is 000000, the UEselects an arbitrary preamble and sets a PRACH mask index to “0” andtransmits the PRACH. The PRACH mask index represents information abouttime/frequency resources available. The information about time/frequencyresources available represents different resources according to aFrequency Division Duplex (FDD) system and a Time Division Duplex (TDD)system.

The second serving cell includes the secondary serving cell. This is sobecause the UE is incapable of initiating the random access procedure inthe secondary serving cell autonomously and the random access procedurecan be started only when a random access initiate indicator is received.In this case, the Cell Indicator Field (CIF) of Table 1 indicates thesecond serving cell where the random access procedure is supposed to beinitiated. The execution order of the steps of S700 and S705 can bechanged, or the steps can be carried out simultaneously.

The UE calculates Estimated-PH (E-PH) estimated in the first subframeS710. The E-PH includes type 1 PH and type 2 PH. The type 1 PH iscalculated by Eq. 1 while the type 2 PH is calculated by Eq. 2.

The UE determines whether the E-PH is less than threshold power P_(th)S715. The threshold power can be 0 dB. For example, if the UE issupposed to transmit the PUSCH only, the UE checks whether the type 1 PHis less than 0 dB. If the UE is supposed to transmit the PUSCH togetherwith the PUCCH, the UE checks whether the type 0 PH is less than 0 dB.Determination by the UE about whether the E-PH is less than 0 dB isequivalent to determining existence of a serving cell where the E-PH inthe first subframe which transmits a PRACH is set to a value less than 0dB.

If the E-PH is less than threshold power, the UE triggers a PHR S720.The PHR is triggered when i) E-PH is less than the threshold power, ii)a periodic timer terminates, iii) an estimate of Path Loss (PL) variesmore than a predetermined reference value, or iv) random accessprocedure indicator with respect to the secondary serving cell isreceived. Since PH varies often, a periodic power headroom reportingmethod can be used. If the periodic timer terminates while the periodicpower headroom reporting method is adopted, the UE triggers powerheadroom reporting. When the power headroom is reported, the UEre-activates the periodic timer. Also, in case the path loss estimatemeasured by the UE varies more than a predetermined reference value,power headroom reporting can be triggered. The path loss estimate ismeasured by the UE on the basis of Reference Symbol Received Power(RSRP). According to one embodiment of the present invention, the stepof S720 can be skipped depending on the situations. In this case, if theestimated power headroom is less than threshold power, the step of S725is carried out immediately. The execution order of the steps of S720 andS725 can be changed, or the steps can be carried out simultaneously. Inthis case, the serving cells included in the power headroom report canbe confined to those serving cells activated at a subframe at which thepower headroom report is measured or those activated serving cells forwhich valid uplink time arrangement values have been secured.

The UE transmits either of the uplink signal and the PRACH selectivelyfrom a first subframe to the BE according to a priority order betweenthe two S725. For example, if the uplink signal has a power allocationpriority higher than the PRACH, the UE transmits the uplink signal tothe first serving cell of the first subframe. On the other hand, if thePRACH has a power allocation priority higher than the uplink signal, theUE transmits the PRACH to the second serving cell of the first subframe.At this time, the UE does not transmit the other one which has a lowerpower allocation priority.

Again, at the step of S715, if the estimated power headroom is largerthan or equal to threshold power, the UE transmits the uplink signal tothe first serving cell of the first subframe while the UE transmits thePRACH to the second serving cell of the first subframe S730.

As described above, if the uplink signal is transmitted selectivelyaccording to a power allocation priority in a multiple component carriersystem, uplink transmission power can be distributed in an efficientmanner. Also, since power allocation is carried out according to asimple and clear rule, system complexity can be reduced, and thus systemperformance can be improved.

FIG. 8 is a flow diagram illustrating a method for controlling uplinktransmission power by a user equipment according to another example ofthe present invention.

With reference to FIG. 8, the UE generates an uplink signal scheduled tobe transmitted on a first serving cell of a first subframe S800. Theuplink signal includes, for example, a physical uplink channel or SRS.The physical uplink channel includes at least one of the PUSCCH and thePUSCH. Two or more serving cells are assigned to the UE, and the firstserving cell includes the primary serving cell.

The UE receives from the BS random access initiate information whichcommands initiation of a random access procedure on a second servingcell of the first subframe S805. The random access initiate informationis related to a second serving cell. The random access initiateinformation is defined in a form similar to the DCI. The DCI is mappedto the PDCCH and transmitted from the BS to the UE, which can be calleda PDCCH order. The DCI can be a DCI format 1A, which is defined as shownin Table 1. The second serving cell includes a secondary serving cell.The execution order of the steps of S800 and S805 can be changed, or thesteps can be carried out simultaneously.

The UE calculates Estimated-PH (E-PH) estimated in the first subframeS810. The E-PH includes type 1 PH and type 2 PH. The type 1 PH iscalculated by Eq. 1 while the type 2 PH is calculated by Eq. 2.

The UE determines whether the E-PH is less than threshold power P_(th)S815. The threshold power can be 0 dB. For example, if the UE issupposed to transmit the PUSCH only, the UE checks whether the type 1 PHis less than 0 dB. If the UE is supposed to transmit the PUSCH togetherwith the PDCCH, the UE checks whether the type 0 PH is less than 0 dB.Determination by the UE about whether the E-PH is less than 0 dB isequivalent to determining existence of a serving cell where the E-PH inthe first subframe which transmits a PRACH is set to a value less than 0dB.

If the E-PH is less than threshold power, the UI triggers a PHR S820. Inother words, the case where the E-PH is less than threshold powercorresponds to a triggering condition for a power headroom report.According to one embodiment of the present invention, the step of S820can be omitted depending on the needs. In this case, if the E-PH is lessthan threshold power, the step of S825 can be carried out immediately.The execution order of the steps of S820 and S825 can be changed, or thesteps can be carried out simultaneously.

The UE adjusts transmission power to be allocated to the uplink signaland the PRACH respectively according to a power allocation priorityS825. For example, if the priority of the uplink signal is lower thanthat of the PRACH, the UE adjusts transmission power of the uplinksignal. More specifically, transmission power of a signal or a channelhaving a low power allocation priority is adjusted on the basis of Table2.

TABLE 2 First serving cell Second serving cell Power allocation priorityPUSCH PRACH PRACH > PUSCH PUSCH(including PUSCH > PRACH ACK/NACK signal,CQI or RI) PUCCH PUCCH > PRACH SRS PRACH > SRS

With reference to Table 2, the power allocation priority of the PEACH ishigher than that of the PUSCH, but in case the ACK/NACK signal isincluded, the power allocation priority of the PUSCH is higher than thatof the PRACH. Also, in case CQI or RI is included in the PUSCH, thepower allocation priority of the PUSCH can be higher than that of thePRACH. The power allocation priority of the PUCCH is higher than that ofthe PRACH, and the PRACH has a higher power allocation priority thanSRS. Table 2 defines power allocation priorities between two channels intwo serving cells, but Table 2 is only an example and the powerallocation priority can be applied equally to the case of three or morechannels in three or more serving cells.

In case three or more channels different from each other are commandedto perform transmission through different serving cells, in other words,in case the PUCCH, PUSCH, and PRACH are transmitted simultaneouslythrough a first, second, and third serving cell, respectively; or thePUCCH and PUSCH are transmitted simultaneously through the first servingcell, and the PRACH is transmitted through the second serving cell, thePUCCH always has a higher priority than the PUSCH.

Transmission power of the uplink signal is adjusted to a valueP′_(PH,c-type1) or P′_(PH,c-type2) specified by the estimated powerheadroom. For example, P′PH,c-type1 can be 0 dB. Adjusting transmissionpower of a signal or a channel having a low power allocation priorityincludes reducing transmission power of a signal or a channel having alow power allocation priority. As one example, Eq. 2 is modified to Eq.4 while Eq. 3 is modified to Eq. 5. This modification reflects the casewhere the uplink signal has a lower power allocation priority than thePRACH.

P′ _(PH,c-type1) =P _(cmax,c) −P′ _(PUSCH,c) [dB]  [Equation 4]

P′ _(PH,c-type2) =P _(cmax,c) −P′ _(PUCCH,c) −P _(PUSCH,c)[dB]  [Equation 5]

In other words, the LIE reduces transmission power of a signal having alow priority to P′_(PUSCH,c) or P′_(PUCCH,c), thereby adjustingestimated power headroom to become P′_(PH,c-type1) or P′_(PH-c-type2).At this time, c is an index of a serving cell and it is equal to 1 (c=1)since an uplink signal is transmitted through the first serving cell. Inthe case of the primary serving cell, c can be zero (c=0) according to adefinition of the serving cell index value.

As another example, Eq. 2 is modified to Eq. 6 while Eq. 3 is modifiedto Eq. 7. This modification reflects the case where the PRACH has alower power allocation priority than the uplink signal. At this time, cis an index of a serving cell and it is equal to 1 (c=1) since an uplinksignal is transmitted through the first serving cell. In the case of theprimary serving cell, c can be zero (c=0) according to a definition ofthe serving cell index value.

P′ _(PH,c-type1) =P′ _(cmax,c) −P _(PUSCH,c) [dB]  [Equation 6]

P′ _(PH,c-type2) =P′ _(cmax,c) −P _(PUCCH,c) −P _(PUSCH,c)[dB]  [Equation 7]

In other words, the UE reduces transmission power of the PRACH having alow priority so that the maximum transmission power becomes P′_(cmax,c).In this way, the HE adjusts estimated power headroom to becomeP′_(PH,c-type1) or P′_(PH,c-type2).

The relationship between reduction of transmission power of the PRACHand reduction of the maximum transmission power can be determined by thefollowing equation.

The maximum transmission power ranges from the minimum valueP_(cmax_L,c) to the maximum value P_(cmax,H,c). Power management MaximumPower Reduction (PMPR) is used as a parameter to determine the minimumvalue P_(cmax_L,c). P_(cmax_L,c) is defined as the following equation.

P _(cmax_L,c)=MIN[P _(Emax,c) −ΔT _(C,c),P_(powerclass)−MAX[MPR_(c)+AMPR_(c), +PMPR_(c) ]−ΔT _(C,c])  [Equation8]

With reference to Eq. 8, PMPRc is a power backoff value (P-MPR) in aserving cell c. MIN[a, b] represents a smaller value between a and b,and P_(Emax,c) represents the maximum power determined by RRC signalingof the BS in the serving cell c. ΔT_(C,c) is an amount of power appliedat the edge of the corresponding frequency band in the case of uplinktransmission, which can be 1.5 dB or 0 dB depending on the frequencybandwidth. P_(powerclass) is a power value according to a few powerclasses defined for supporting specifications of various types of UEs ina multiple component carrier system. In general, the LTE system supportspower class 3, and P_(powerclass) according to the power class 3 is 23dBm, MPRc is an amount of maximum power reduction in the serving cell c,and Additional MPRc (AMPRc) is an additional amount of maximum powerreduction signaled by the BS in the serving cell c.

As described above, the maximum transmission power P_(cmax,c) in eachserving cell is changed by the PMPRc. If the maximum transmission powerP_(cmax,c) in each serving is changed, power headroom is eventuallychanged, too.

As one example, the following equation determines PMPR of a servingcell.

$\begin{matrix}{{{PMPR}_{c} = {\frac{{\sum P_{c{max\_ etc}}} + P_{PRACH}}{N - M} + {EMPR}_{c}}},} & \left\lbrack {{Equation}\mspace{14mu} 9} \right\rbrack\end{matrix}$

where PMPRc is PMPR of a serving cell c; ΣP_(cmax,etc) is a total sum ofcurrent transmission power of a wireless communication system excludingthe LTE system P_(PRACH) is a transmission power value to be allocatedto the PRACH that can be transmitted in the random access procedure;EMPRc is an additional maximum transmission power reduction value(E-MPR) to reduce a unique emission effect due to the LTE frequency bandof the corresponding serving cell c. N is the number of serving cellsincluding the UL CC, allocated to the UE which has received randomaccess initiate information in an arbitrary, active serving cell; and Mis the number of serving cells within a Timing Alignment Group (TAG)which has failed to secure a valid Timing Alignment (TA) value or whichhas secured the TA value, validity of which has been expired. In otherwords, N-M represents the number of serving cells included in the TAGSwhich have secured valid. TA values among serving cells including the ULCC allocated to the UE which has received a PDCCH command in anarbitrary, active serving cell.

As another example, the transmission power value P_(PRACH) to beallocated to the PRACH that can be transmitted during the random accessprocedure can be determined on the basis of preamble received targetpower. Taking account of an estimate of the UE's downlink to path loss,P_(PRACH) can be determined by the following equation so that it may notexceed the Pcmax,c value.

P _(PRACH)=min[P _(cmax,c)(i), PRTP+PL_(c)] [dB],  [Equation 10]

where P_(cmax,c)(i) is transmission power of the UE configured withrespect to a subframe i of a serving cell; and PLc is an estimate of theUE's downlink path loss with respect to the serving cell. PRTP ispreamble received target power.

The UE, based on a power allocation priority, can reduce P_(PRACH),which denotes transmission power of the PRACH having a low priority, andaccordingly, PMPR is reduced, thereby eventually reducing P_(cmax,c).

On the other hand, the P_(PRACH) value may not be reflected in the PMPRvalue, but can be defined as a value affecting P_(cmax,c) valuedirectly. In other words, the P_(PRACH) can be defined so that theP_(cmax,c) reduces the P_(PRACH) by P_(PRACH)/(N-M) directly withrespect to the serving cells which have been activated and have secureduplink time alignment values. The UE transmits the uplink signal to theBS through a first serving cell of a first subframe based on adjustedtransmission power and transmits the PRACH through a second serving cellof the first subframe S830, In the case of a low power allocationpriority, too, the uplink signal or the PRACH can be transmitted withreduced transmission power.

Again, at the step of S815, if the estimated power headroom is largerthan or equal to threshold power, the UE transmits the uplink signal tothe first serving cell of the first subframe without adjustment oftransmission power while the UE transmits the PRACH to the secondserving cell of the first subframe S830.

In this manner, at the time of transmitting an uplink signal in amultiple component carrier system, if transmission power of eachphysical uplink channel or signal is adjusted according to a powerallocation priority, transmission of a particular signal can be alltransmitted without being dropped.

FIG. 9 is a flow diagram illustrating a method for controlling uplinktransmission power according to one example of the present invention.

With reference to FIG. 9, the BS transmits a random access initiateinformation on a second serving cell of a first subframe, which commandsinitiation of a random access procedure, to the UE S900. A first servingcell SCell 1 and a second serving cell SCell 2 are linked to the UE, andin this example, the random access initiate information is transmittedto the first serving cell. The random access initiate information canalso be transmitted to the second serving cell. The random accessinitiate information includes a DCI format 1A as shown in Table 1 and acell index field specifies the second serving cell. At this time, thefirst serving cell can be the primary serving cell, and the secondserving cell can be the secondary serving cell.

The UE calculates Estimated-PH (E-PH) S905. The E-PH includes type 1 PHand type 2 PH. The type 1 PH is calculated by Eq. 1 while the type 2 PHis calculated by Eq. 2. At this time, it is assumed that the E-PH isless than a particular value (for example, 0 dB).

Since the E-PH is less than a particular value, the UE triggers a PowerHeadroom Report (PHR) S910.

If there exist a PUSCH to be transmitted to the first serving cell ofthe first subframe, the UE determines a power allocation prioritybetween the PUSCH and a PRACH to be transmitted to the second servingcell. For example, if the PUSCH includes none of the ACK/NACK signal,CQI, and RI, the UE determines that the PUSCH has a lower priority thanthe PRACH and reduces transmission power of the PUSCH according to Eq. 4so that the E-PH becomes 0 dB. And the UE transmits the PUSCH to the BSthrough the first serving cell of the first subframe by using reducedtransmission power and transmits the PRACH to the BS through the secondserving cell of the first subframe by using the originally scheduledtransmission power S915.

Next, the UE transmits the PHR to the BS S920. This is intended toinform the BS that the PH is less than 0 dB so that the BS performsagain the random access initiation or uplink scheduling.

FIG. 10 is a block diagram illustrating a user equipment and a basestation controlling uplink transmission power according to one exampleof the present invention.

With reference to FIG. 10, the UE 1000 comprises a reception unit 1005,a UE processor 1010, and a transmission unit 1020. The UE processor 1010again comprises a power adjustment unit 1011 and a signal generationunit 1012.

The reception unit 1005 receives random access initiate information fromthe BS 1050. The random access initiate information is related to asecond serving cell established for the UE 1000. The random accessinitiate information includes Downlink Control Information (DCI). TheDCI is mapped to the PUCCH and transmitted from the BS to the UE, whichcan be called a PDCCH order. The DCI can be a DCI format 1A, which canbe defined as shown in Table 1.

The power adjustment unit 1011 calculates Estimated-PH (E-PH) estimatedin the first subframe. At this time, the first subframe denotes a timeinterval through which a physical uplink channel or signal istransmitted to the first and the second serving cell configured for theUE 1000. The E-PH includes type 1 PH and type 2 PH. The type 1 PH iscalculated by Eq. 1 while the type 2 PH is calculated by Eq. 2.

The power adjustment unit 1011 determines whether the E-PH is less thanthreshold power P_(th). The threshold power can be 0 dB. For example, ifthe UE 1000 is supposed to transmit the PUSCH only, the power adjustmentunit 1011 checks whether the type 1 PH is less than 0 dB. If the UE 1000is supposed to transmit the PUSCH together with the PUCCH, the UE checkswhether the type 0 PH is less than 0 dB. Determination by the poweradjustment unit 1011 about whether the E-PH is less than 0 dB isequivalent to determining existence of a serving cell where the E-PH inthe first subframe which transmits a PRACH is set to a value less than 0dB.

If the E-PH is less than threshold power, the signal generation unit1012 triggers a PHR. In other words, the case where the E-PH is lessthan threshold power corresponds to a triggering condition for a powerheadroom report.

The signal generation unit 1012 generates the uplink signal and thePRACH. The uplink signal includes at least one of the PUSCH, PUCCH, andSRS. The uplink signal is scheduled to be transmitted to the firstserving cell while the PRACH is scheduled to be transmitted to thesecond serving cell.

The power adjustment unit 1011 adjusts transmission power to beallocated to the uplink signal and the PRACH respectively according to apower allocation priority. For example, if the priority of the uplinksignal is lower than that of the PRACH, the power adjustment unit 1011adjusts transmission power of the uplink signal. More specifically, thepower adjustment unit 1011 adjusts transmission power of a signal or achannel having a low power allocation priority on the basis of Table 2.And the power adjustment unit 1011 controls the transmission unit 1020so that the uplink signal can be transmitted based on the adjustedtransmission power.

Similarly, the power adjustment unit 1011 selects either of the uplinksignal and the PRACH based on a power allocation priority and allocatestransmission power to the selected one according to the originalschedule but does not allocate transmission power to the other. In otherwords, the power adjustment unit 1011 drops transmission of the otherone. To this end, the power adjustment unit 1011 controls thetransmission unit 1020 so that only the selected one can be transmitted.

The transmission unit 1020 transmits the uplink signal and the PRACHbased on the transmission power adjusted respectively according to thecontrol of the power adjustment unit 1011, where the uplink signal istransmitted to the first serving cell of the first subframe and thePRACH is transmitted to the second serving cell of the first subframe.Similarly, the transmission unit 1020 transmits either of the uplinksignal and the PRACH selected according to the control of the poweradjustment unit 1011. For example, in case the uplink signal isselected, the transmission unit 1020 transmits the uplink signal to thefirst serving cell of the first subframe. On the other hand, in case thePRACH is selected, the transmission unit 1020 transmits the PRACH to thesecond serving cell of the first subframe.

If the E-PH is larger than or equal to threshold power, the poweradjustment unit 1011 allocates and distributes the transmission powerscheduled originally in the first subframe for transmission of theuplink signal and the PRACH; and the transmission unit 1020 transmitsthe uplink signal and the PRACH generated by the signal generation unit1012 to the BS 1050.

The BS 1050 comprises a transmission unit 1055, a reception unit 1060,and a BS processor 1070. The BS processor 1070 again comprises a DCIgeneration unit 1071 and a scheduling unit 1072.

The transmission unit 1055 transmits random access initiate informationto the UE 1000.

The reception unit 1060 receives at least one of the uplink signal andthe PRACH from the UE 1000. At this time, the reception unit 1060receives the uplink signal from the first serving cell and receives thePRACH from the second serving cell. Sometimes the reception unit 1060can operate in a Discontinuous RX (DRX) mode at which signaldiscontinuity of the UE is determined.

The DCI generation unit 1071 generates random access initiateinformation and transmits the generated information to the transmissionunit 1055.

The scheduling unit 1072 schedules transmission of the uplink signal ofthe UE 1000.

The descriptions above are only illustration of the technical principlesof the present invention, and it should be noted by those skilled in theart to which the present invention belongs that various modificationsand changes are possible without departing from the inherentcharacteristics of the present invention. Therefore, the embodimentsdisclosed in this document are not intended to limit the technicalprinciples of the present invention but are intended for descriptionthereof; and the technical scope of the present invention is not limitedby the embodiments. The technical scope of the present invention shouldbe interpreted by the appended claims, and it should be understood thatall of the technical principles falling within the range equivalentthereto are included in the technical scope of the present inventiondefined by the appended claims.

1. A communication method performed by a user equipment, comprising:generating an uplink signal to be transmitted on a first serving cell;generating a random access preamble to be transmitted on a secondserving cell; calculating a summation of a first power and a secondpower; determining an adjusted power to transmit the uplink signal basedon the summation of the first power and the second power; transmitting,to an evolved-NodeB (eNB), the uplink signal on the first serving cellusing the adjusted power; and transmitting, to the eNB, the randomaccess preamble on the second serving cell using the second power. 2.The method of claim 1, further comprising receiving, from the eNB,random access initiate information commanding initiation of a randomaccess procedure, wherein the random access initiate informationincludes an index of the random access preamble.
 3. The method of claim1, wherein the adjusted power is determined by comparing the summationof the first power and the second power with a threshold value.
 4. Themethod of claim 1, wherein the uplink signal is transmitted through aPhysical Uplink Control Channel (PUCCH).
 5. The method of claim 1,wherein the uplink signal is transmitted through a Physical UplinkShared Channel (PUSCH).
 6. The method of claim 1, wherein the uplinksignal comprises a Sounding Reference Signal (SRS).
 7. The method ofclaim 1, wherein the uplink signal comprises at least one of an ACK/NACKsignal, Channel Quality Information (CQI), and a rank indicator.
 8. Acommunication apparatus comprising: a memory; and a processor operablycoupled to the memory, wherein the processor, when executing programinstructions stored in the memory, is configured to: generate an uplinksignal to be transmitted on a first serving cell; generate a randomaccess preamble to be transmitted on a second serving cell; calculate asummation of a first power and a second power; determine an adjustedpower to transmit the uplink signal based on the summation of the firstpower and the second power; cause the communication apparatus totransmit, to an evolved-NodeB (eNB), the uplink signal on the firstserving cell using the adjusted power; and cause the communicationapparatus to transmit, to the eNB, the random access preamble on thesecond serving cell using the second power.
 9. The communicationapparatus of claim 8, wherein the processor is further configured tocause the communication apparatus to receive, from the eNB, randomaccess initiate information commanding initiation of a random accessprocedure, wherein the random access initiate information includes anindex of the random access preamble.
 10. The communication apparatus ofclaim 8, wherein the adjusted power is determined by comparing thesummation of the first power and the second power with a thresholdvalue.
 11. The communication apparatus of claim 8, wherein the uplinksignal is transmitted through a Physical Uplink Control Channel (PUCCH).12. The communication apparatus of claim 8, wherein the uplink signal istransmitted through a Physical Uplink Shared Channel (PUSCH).
 13. Thecommunication apparatus of claim 8, wherein the uplink signal comprisesa Sounding Reference Signal (SRS).
 14. The communication apparatus ofclaim 8, wherein the uplink signal comprises at least one of an ACK/NACKsignal, Channel Quality Information (CQI), and a rank indicator.
 15. Adevice for a user equipment (UE) comprising: a memory; and a processoroperably coupled to the memory, wherein the processor, when executingprogram instructions stored in the memory, is configured to: generate anuplink signal to be transmitted on a first serving cell; generate arandom access preamble to be transmitted on a second serving cell;calculate a summation of a first power and a second power; determine anadjusted power to transmit the uplink signal based on the summation ofthe first power and the second power; cause the UE to transmit, to anevolved-NodeB (eNB), the uplink signal on the first serving cell usingthe adjusted power; and cause the UE to transmit, to the eNB, the randomaccess preamble on the second serving cell using the second power. 16.The device of claim 15, wherein the processor is further configured tocause the UE to receive, from the eNB, random access initiateinformation commanding initiation of a random access procedure, whereinthe random access initiate information includes an index of the randomaccess preamble.
 17. The device of claim 15, wherein the adjusted poweris determined by comparing the summation of the first power and thesecond power with a threshold value.
 18. The device of claim 15, whereinthe uplink signal is transmitted through a Physical Uplink ControlChannel (PUCCH).
 19. The device of claim 15, wherein the uplink signalis transmitted through a Physical Uplink Shared Channel (PUSCH).
 20. Thedevice of claim 15, wherein the uplink signal comprises at least one ofan ACK/NACK signal, Channel Quality Information (CQI), and a rankindicator.